Does Google still support the robots.txt noindex directive?
No, back in September 2019 Google stopped supporting the unofficial robots.txt noindex directive.
While its use should have always been a last resort, the directive is completely useless now.
What about other search engines you ask, like Bing for instance? They've (opens in a new tab).
Audit your robots.txt and find out so you can correctly noindex content!
So what's the best way to noindex pages?
The best way to noindex pages is to use the meta robots tag or X-Robots-Tag.